Active-space completely-renormalized equation-of-motion coupled-cluster formalism: Excited-state studies of green fluorescent protein,free-base porphyrin, and oligoporphyrin dimer

• Published in: The Journal of chemical physics 2010-04, Vol.132 (15), p.154103-154103-11
• Main Authors: Kowalski, Karol, Krishnamoorthy, Sriram, Villa, Oreste, Hammond, Jeff R., Govind, Niranjan
• Format: Article
• Language: English
• Subjects: Algorithms; BENCHMARKS; calculations; CORRELATIONS; Dimerization; DIMERS; ELECTRONIC STRUCTURE; electronic structure methods; ELECTRONS; Environmental Molecular Sciences Laboratory; Equation-of-Motion Coupled Cluster; EXCITATION; excitations; EXCITED STATES; FUNCTIONS; Green Fluorescent Proteins - chemistry; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; PORPHYRINS; Porphyrins - chemistry; Quantum Theory
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.3385315

The completely renormalized equation-of-motion coupled-cluster approach with singles, doubles, and noniterative triples [CR-EOMCCSD(T)] has proven to be a reliable tool in describing vertical excitation energies in small and medium size molecules. In order to reduce the high numerical cost of the genuine CR-EOMCCSD(T) method and make noniterative CR-EOMCCSD(T) approaches applicable to large molecular systems, two active-space variants of this formalism [the CR-EOMCCSd(t)-II and CR-EOMCCSd(t)-III methods], based on two different choices of the subspace of triply excited configurations employed to construct noniterative correction, are introduced. In calculations for green fluorescent protein (GFP) and free-base porphyrin, where the CR-EOMCCSD(T) results are available, we show good agreement between the active-space CR-EOMCCSD(T) (variant II) and full CR-EOMCCSD(T) excitation energies. For the oligoporphyrin dimer ( P 2 TA ) active-space CR-EOMCCSD(T) results provide reasonable agreement with experimentally inferred data. For all systems considered we demonstrated that the active-space CR-EOMCCSD(T) corrections lower the EOMCCSD (iterative equation-of-motion coupled-cluster method with singles and doubles) excitation energies by 0.2 and 0.3 eV, which leads to a better agreement with experiment. We also discuss the quality of basis sets used and compare EOMCC excitation energies with excitation energies obtained with other methods. In particular, we demonstrate that for GFP and FBP Sadlej's TZP and cc-pVTZ basis sets lead to a similar quality of the EOMCC results. The performance of the CR-EOMCCSD(T) implementation is discussed from the point of view of timings of iterative parts and scalability of the most expensive, N 7 , part of the calculation. In the latter case the scalability across 34008 processors is reported.